A work machine may be used to move heavy loads, such as earth, construction material, and/or debris, and may include, for example, a wheel loader, an excavator, a front shovel, a bulldozer, a backhoe, and a telehandler. The work machine may utilize a work implement to move the heavy loads. The work implement of the work machine may be powered by a hydraulic system that may use pressurized fluid to actuate a hydraulic actuator to move the work implement.
During operation of the work machine, the implement may be raised to an elevated position. As the implement may be relatively heavy, the implement may gain potential energy when raised to the elevated position. As the implement is released from the elevated position, this potential energy may be converted to heat when pressurized hydraulic fluid is forced out of the hydraulic actuator and is throttled across a valve and returned to a tank. Typically, the conversion of potential energy into heat may result in an undesired heating of the discharged hydraulic fluid, which may require that the work machine possess additional cooling capacity. Recovering that lost or wasted potential energy for reuse may improve work machine efficiency.
One system designed to recover or recycle the energy associated with lowering a load is disclosed in U.S. Pat. No. 7,269,944. The hydraulic circuit disclosed in that reference includes a hydraulic cylinder and a pump configured to supply hydraulic fluid to the hydraulic actuator. The hydraulic circuit also includes an energy recovery system operatively connected between the hydraulic actuator and the pump that is configured to store pressurized fluid from the hydraulic actuator under an overrunning load condition. The energy recovery system can include a high pressure accumulator, a tank accumulator, a high pressure charge valve and a high pressure discharge valve. The hydraulic circuit further includes a control valve assembly including two pump-to-cylinder independent metering control valves and two cylinder-to-tank independent metering control valves. A disadvantage associated with this hydraulic circuit is the number of control valves and the use of two accumulators, which can increase the complexity of the hydraulic circuit.